Individual consistency and sex differences in migration strategies of Scopoli’s shearwaters Calonectris diomedea despite year differences

Abstract

Recently-developed capabilities for tracking the movements of individual birds over the course of a year or longer has provided increasing evidence for consistent individual differences in migration schedules and destinations. This raises questions about the relative importance of individual consistency versus flexibility in the evolution of migration strategies, and has implications for the ability of populations to respond to climatic change. Using geolocators, we tracked the migrations of Scopoli’s shearwaters Calonectris diomedea breeding in Linosa (Italy) across three years, and analysed timing and spatial aspects of their movements. Birds showed remarkable variation in their main wintering destination along the western coast of Africa. We found significant individual consistency in the total distance traveled, time spent in transit, and time that individuals spent in the wintering areas. We found extensive sex differences in scheduling, duration, distances and destinations of migratory journeys. We also found sex differences in the degree of individual consistency in aspects of migration behaviour. Despite strong evidence for individual consistency, which indicates that migration journeys from the same bird tended to be more similar than those of different birds, there remained substantial intra-individual variation between years. Indeed, we also found clear annual differences in departure dates, return dates, wintering period, the total distance traveled and return routes from wintering grounds back to the colony. These findings show that this population flexibly shifts migration schedules as well as routes between years in response to direct or indirect effects of heterogeneity in the environment, while maintaining consistent individual migration strategies.

Flexibility in otherwise consistent non-breeding movements of a long-distance migratory seabird, the long-tailed skua

“…This shows an intriguing combination of general site fidelity and flexibility in subsequent winter movements. High winter area fidelity has been shown in several seabird species from several families, using both GPS and light-based tracking devices (Phillips et al 2005, Guilford et al 2011, Muller et al 2013, McFarlane Tranquilla et al 2014, Yamamoto et al 2014. With generally high route consistency within staging areas throughout the winter months, long-tailed skuas fit to this pattern, although their movements are often not restricted to a single, welldefined area (i.e.…”

Consistent variation in individual migration strategies of brown skuas

“…This could ultimately lead to variation in individual migration patterns of seabirds at some spatial scale across years. Indeed, although most species show high individual consistency in non-breeding destinations at a large spatial scale (Phillips et al 2005, Müller et al 2014, there are exceptions; in addition, in almost all species there is extensive variation both among and within individuals in routes, use of staging areas and timing (Quillfeldt et al 2010, Dias et al 2011, McFarlane Tranquilla et al 2014.…”

Methods for detecting and quantifying individual specialisation in movement and foraging strategies of marine predators

“…Biologging studies can be used to assess the potential specialisation or flexibility of individuals from within a population because individuals can be tracked across multiple trips or over the course of a year or longer (Pinaud & Weimerskirch 2005, Soanes et al 2013, Muller et al 2014. As such, the data can be used to examine repeatability in foraging destinations (i.e.…”

“…The most common summary data derived from each trip that have been used in this way include the total duration, total distance travelled (summed great circle distances between fixes), maximum range (great circle distance to the furthest location), and bearing at departure or to the furthest point (Hamer et al 2001, 2007, Soanes et al 2013, Ceia et al 2014, Patrick et al 2014, Baylis et al 2015b, Oppel et al 2015, Potier et al 2015. For the non-breeding season, the analyses are often of migration schedules (timing and duration of events; Croxall et al 2005, Dias et al 2011, Yamamoto et al 2014, or the total distance travelled during the migration (Muller et al 2014). Other 1-dimensional data used in studies of individual specialisation include dive characteristics and activity metrics (Laidre et al 2002, Staniland et al 2004, Cook et al 2006, Ratcliffe et al 2013, Patrick et al 2014, Potier et al 2015, Wakefield et al 2015.…”

“…This method has been used to compare foraging areas in consecutive trips during the breeding season , Pettex et al 2012, Soanes et al 2013, and areas used from one year to the next (Chilvers 2008, McFarlane Tranquilla et al 2014, Muller et al 2014). The problem is that it does not exploit the information on the complete UDs (cf.…”